Ad-libbing while leading in prayer during a worship service is not a great practice, though one I've been guilty of frequently enough. This book is intended to help those leading in worship (which I dearly hope are pastors, or at least elders; no separate "worship leader" on staff, please!) as they plan prayers. Quinn (a long-term staff member at University Reformed Church in East Lansing) leads us through various elements of prayer, and then provides lots and lots of examples in the second half of the book. Thus this will be an important reference work as well as a pedagogical tool.
A few of the prayers sound off, as does a small portion of the advice (such as not wanting to sound like you're reading a prayer; if you're reading a prayer, there is nothing wrong with it sounding as such!). But all in all this is an excellent resource that pastors should utilize as they seek to lift their corporate prayer over the banal, repetitive, and self-centered.